Station and method for operating a CAN communication line

Abstract

A CAN communication line is operated whilst detecting a ground level shift on the communication line through storing a data element indicative for the shift. In particular, a current line voltage level is compared to a standard level, and a thresholded version of the comparison is fed to a storage element that is triggered by a local transmission indicator signal. Then a ground shift sample bit from the storage element is outputted.

1. A method of operating a Controller Area Network communication line, comprising:
 comparing a first Controller Area Network bus line having a first voltage thereon, to a ground level; 
 generating a first signal, where the first signal is a logic “1” if the difference between the first Controller Area Network bus line and the ground level is less than a first voltage; and the first signal is a logic “0” if the difference between the first Controller Area Network bus line and the ground level is greater than the first voltage; 
 selecting the first signal as an input signal to an edge-triggered flip-flop if a receive data signal is in a first one of two states, and selecting an output signal of the edge-triggered flip-flop as an input signal to the edge-triggered flip-flop if the receive data signal is in a second one of two states; and 
 clocking the edge-triggered flip-flop when a transmit data signal changes state. 
 
     
     
       2. The method of  claim 1 , wherein the first voltage is −1.2 volts. 
     
     
       3. The method of  claim 1 , wherein the first voltage has a tolerance in the region of 320%. 
     
     
       4. The method of  claim 1 , the edge-triggered flip-flop is a positive edge-triggered flip-flop, and the edge-triggered flip-flop is clocked when the transmit data signal changes state from a high level to a low level. 
     
     
       5. An apparatus for operating a Controller Area Network communication line, comprising:
 a means for comparing a first Controller Area Network bus line having a first voltage thereon, to a ground level; 
 a means for generating a first signal, where the first signal is a first logical value if the difference between the first Controller Area Network bus line and the ground level is less than a first voltage; and the first signal is a second logical value, if the difference between the first CAN bus line and the ground level is greater than the first voltage; 
 a means for selecting the first signal as an input signal to an edge-triggered flip-flop if a receive data signal is in a first one of two states, and selecting an output signal of the edge-triggered flip-flop as an input signal to the edge-triggered flip-flop if the receive data signal is in a second one of two states; and 
 a means for clocking the edge-triggered flip-flop when a transmit data signal changes state. 
 
     
     
       6. The apparatus of  claim 5 , wherein the first voltage is −1.2 volts. 
     
     
       7. The apparatus of  claim 5 , wherein the first voltage has a tolerance in the region of 320%. 
     
     
       8. The apparatus of  claim 5 , wherein the first logical value is “1” and the second logical value is “0”. 
     
     
       9. The apparatus of  claim 5 , wherein the clocking of the edge-triggered flip-flop occurs responsive to a high-to-low transition of the transmit data signal.